Electric arc discharge lamp



Dec. 26, 1939. Q w, HANSELL, 2,184,386

l ELECTRIC ARC DISCHARGE LAMP Filed Dec. 24, 1937 3 SheeiS-Sheet l x Nl:

ATTORNEY.

Dec. 26, 1939. c. w. HANSELL.

ELECTRIC ARC DISCHARGE LAMP Filed Deo. 24, 19:57 `5 sheets-snee; 2

-HHH 4.aPOWER /NPUT INVENTOR. .m MAA/SELL ATTORNEY.

Dec. 26, 1939. c. w. HANSELL ELECTRIC ARC DISCHARGE LAMP 3 Sheets-Sheet 3 Filed Dec.

IIIIIIIII .SECND ANODE AMPERES INVENTOR. M C'. W HANSELL BYl A TTORNEY.

Patented Dec. 26, 1939 ELECTRIC ARC DISCHARGE LAMP Clarence W. Hansell, Port Jeerson, N. Y., assignor to Radio Corporation of America, a corporation oi.' Delaware Application December 24, 1937, Serial No. 181,505

16 Claims.

This invention relates to electrical arc discharges in low pressure gases and vapors and has for an object to produce a new and improved form of electrical arc discharge lamp. Another object is to provide an eilicient arc discharge lamp which will operate with a mixture of gases to obtain new color eiects. Still another object is to produce a mercury arc discharge lamp giving a relatively intense white light. This invention is based upon studies and experiments with electrical discharges through holes and barriers between chambers containing gas or vapor at low pressure. I have discovered that arcs through holes in metal barriers have peculiar properties not exhibited by ordinary arc discharges and I make use of these properties in my present invention. This discovery was made as a result of my own experiments conducted with electrical vacuum pumps of the general type `described in my United States Patents No. 2,022,465, No. 2,063,249 and No. 2,063,250, and other devices involving electrical discharges through holes and orices.

According to one embodiment of my present invention two or more low pressure gas or vapor lled chambers are separated from one another by one or more metal barriers with holes therein, the chamber at one end being provided with an anode and the chamber at the other end being provided with a cathode and containing mercury. If an arc discharge is established between the cathode and the anode through the barrier, or barriers, I find that the arc in line with the hole in the barrier and through the hole loses its characteristic mercury arc color and appears as a conical source of relatively intense and relatively white light. By increasing the current in the arc a critical value of current is found beyond which the current remains nearly con- 40 stant but the voltage drop in the arc increases.

In other words, there is a denitely limited current which can be passed through the hole in the steel barrier, the value of current depending chiefly upon the mercury vapor pressure and the dimensions of the hole, but hardly at all upon the voltage so long as the voltage is equal to or above the minimurr arc drop through the hole. Usually, the arc drop between the cathode and anode through the hole in the barrier is found to remain nearly constant at about 35 volts almost regardless of arc current and vapor pressure up to the limiting value after which the current remains substantially constant even if the voltage between the cathode and anode is increased up to 350 volts, or more.

I believe that the change in color of the light emitted by the arc through the hole in the steel plate and which diifers so greatly from the blue green light, which is characteristic of the usual low pressure mercury arc, is brought about prin- 5 cipaly by the change in voltage drop in the arc.

I have found that the ordinary voltage drop in an arc between a mercury pool cathode and an anode, without the barrier, may be on the order of l0 to l5 volts depending upon the dimensions 10 and the vapor pressure and is substantially independent of the current in the arc over any reasonable range of current. I have found it so for any current up to amperes, in my experiments, which was the maximum value permitted by my 15 power source; and the experience of others, with large mercury arc rectiers indicates also that the voltage drop can remain low for currents up to thousands of amperes.

However, as soon as we interpose a barrier and 20 pass the' arc through a hole in the barrier, the arc drop is immediately increased to about 35 volts even without current limiting. Even this increase in arc drop is sufllcient to cause multiple or double ionization of the mercury and to 25 greatly increase the equivalent temperature of a portion of the mercury vapor in the path of the arc. As a result, the light from the vapor in the path of the arc through the hole is greatly increased in intensity and apparent whiteness. 30 As the current is increased the intensity of the f light and its whiteness increases rapidly and the length of the streamer of flame issuing from the hole increases toward the cathode. After current limiting sets in the length of flame and 35 the color and intensity of light continue to change as the voltage is raised.4

Turning, now, to another aspect of my invention, it has frequently been proposed to employ mixtures of gases or vapors in glow or arc dis- 4i) charge lamps in order to combine the color spectrums of the gases or vapors to obtain new color effects and to obtain more nearly white light. For example, argon and helium produce spectra which, when added together in proper ratio, 45 would give a reasonably white light. Except to a limited degree, such proposals have not led to successful results, as far as I am aware, because it is found that the gas or vapor which ionizes most easily carries nearly all the current in the 50 arc and the other gases or vapors are frequently substantially non-ionized. In an argon-helium mixture, for example, the argon would continue to carry nearly all the current and to produce nearly all the light. The reason is that electron and production of light.

and ion velocities sumcient to cause enough ionization of the easily ionizable gas to maintain space charge balance are reached without attaining velocities high enough to ionize the other gases present. The only gaseous mixtures which are capable of being used together to add the light spectrums are those which have very nearly equal ionization potentials such as helium and neon. If the ionization potentials are far apart, as in the case of helium and argon, then the gas or vapor which is hard to ionize contributes little, if anything, to the total ionization My present invention, however, overcomes this limitation to the control of spectrum distribution in gaseous discharge lamps by increasing the overall potential and potential gradients in the path of the discharge. High electron and ion velocities are established in the path of the discharge through a hole in a barrier and these velocities can be high enough to cause ionization of any of the gases or vapors present and, therefore, to produce light spectrums corresponding to gases which are hard to ionize, as well as those which ionize easily.

In order that others skilled in the art may be given sufllcient information to practice my invention, several specific examples are illustrated in the drawings and will now be described.

In the accompanying drawings Fig. 1 is a cross-sectional view of a device employing the features and principles of my invention and the wiring diagrams and connections therefor. Figs. 2 and 3 illustrate modifications of my invention which are somewhat more compact and more readily utilizable. Figs. 4 and 5 illustrate modiiications of my invention having a plurality of barrier anodes for further increasing the voltage drop through the tube. Fig. 6 illustrates a further modication of my invention and especially designed for full-wave operation, while Fig. 7 is a graph explanatory of my present invention.

Referring to Fig. l, which is the drawing of an experimental mercury arc tube which I have used and the circuits associated therewith. there is shown an outer envelope which was obtained by altering a standard 4 inch pipe cross. Ihis pipe cross has four openings. Over one of the openings is fitted a blank plate 3 held in place by bolts 5 and over the diametrically opposite opening is .tted a high temperature glass or a quartz plate 1 held in place by steel flange 9 and bolts Ii. an assembly including insulators I3 and I1, steel ring I5 and steel flange I9, all held tightly in place by insulated bolts 2|. An additional plate 23 is provided to serve as a mounting plate and is suitably attached to plate I9. Over the upper opening is provided insulator 21. a steel ring 29. a second insulator 3| held tightly in place by bolts 35. lated from the ring and flange To seal all joints the surfaces are accurately fitted together and joined by means of gaskets of thin varnished silk, thus making a hermetically sealed container. The container is evacuated through connection 39, a water cooled condenser trap 4I, connection .45 and vacuum pump 41. A mercury vacuum gauge is connected to connection 45.

Held in a depression in pool 49 which serves as a this pool of mercury is a short cylinder of high temperature glass'l, the function of which is to restrict the arc to the area of the mercury surange I9 is a mercury cathode. Standing in Over the lower opening is fittedface within the cylinder. Connected with ring Il is an arc starter point 53 made of a carborundum compound commonly known as 'I'hyrite. This point is mounted so that its tip is within about of an inch from the surface of the mercury. Mounted on steel ring 29 is a first anode 55 consisting of a steel cylinder closed at the lower end with a steel plate 55a. Through this -steel plate is a hole 51. Mounted on steel flange 33 is a cylindrical second anode 59, the end of which is located immediately over hole 51. This second anode has a drilled hollow at the end, the depth of which may be varied as desired. The function of this hollow is to distribute the power losses at the second anode over a larger area and to assist in controlling the behavior of the arc.

A D. C. generator |0| is provided which supplies power through switch |03 and a current limiting resistance |05 to the first anode 55. A second D. C. generator |01 supplies power through switch |09, variable resistance III, reactance or choke ||1 and a second load reactance |I3 to the second anode 59.

A large condenser ||5 and a surge arrestor I|9 are used to keep high frequency transient currents out of the generator circuit. 'I'he surge arrestor ||9 may be composed of a material having a resistance which decreases rapidly with increase in the voltage applied thereto, such as 'Ihyrite." A load resistance consisting of incandescent or gaseous discharge lamps |2| is connected across reactor II3.

For starting the arc a transformer I 23 is provided which is supplied with cycle, 110 volt A. C. power through push button switch |25. The transformer, which is of the type commonly employed in oil burner heating systems for ignition, develops an open circuit A. C. voltage of about 15,000 volts but is designed to have a high leakage reactance and secondary resistance so that the secondary current is always limited to a low value. A transformer for neon lamp excitation has similar characteristics and could as well be used. The secondary winding of the transformer is connected between steel flange I9 and steel ring I5 and through these applies the 15,000 volts starting potential across the small gap between the starter point 53 and mercury pool 49 within the isolating cylinder 5|. By applying potential to first anode 55 and then momentarily energizing transformer |23 by closing switch |25, it is possible to start an arc between the first anode and the mercury pool. This arc will continue indefinitely as long as power is supplied and is the means for maintaining continuous ionization in the chamber between the first anode and cathode.

By closing switch |09 a current can be drawn through the hole 51 to the second anode 59. This current can be varied at will by varying the value oi' resistance III and the voltage of generator I 01 from a value of a few milliamperes up to a critical limiting value ranging from l to 50 amperes in one particular case, depending upon dimensions of the hole 51 and the gas or vapor pressure in the vicinity of the hole.

After the critical or limiting value of current is reached any further attempt to increase the` current results substantially in only increasing the voltage drop between the mercury pool cathode and the second anode. Fig. '7 is a typical measured current versus voltage characteristic of a mercury arc through a hole, measured with the arc discharge device illustrated in Fig. l.

It will be noted that passage of the arc through the hole in the metal plate has increased the arc drop from the normal low value of, say, 13 volts up to about 35 volts for all currents ranging from 0.1 to 5 amperes. 'I'his increased arc drop is sufiicient to cause ionization of any kind of gas in the path of the arc and also to cause double ionization of the more easily ionized gases. As a result the color and intensity of the light in the path of the arc are considerably modified. The arc gives a more brilliant and a whiter light as a result of the increased voltage drop. If the current through the arc is suiciently increased limiting of the current takes place. In Fig. 7 'limiting is shown at about 7 amperes. The increasing voltage after limiting, as shown in Fig. 7, results in an increase in the brilliancy of the light emitted by the mercury arc and its apparent whiteness, as heretofore explained, but the increase in light is less than might be expected because strong limiting has always been accompanied by oscillations or rapid starting and stopping of anode current through the hole. Therefore, even after limiting, the current flows through the arc without rr' ch increase above 35 volts in the instantaneous voltage drop during current pulses.

The device of Fig. l, while it enable me to observe the effects and characteristics of arcs through holes, including the effect upon emitted light. is not particularly adapted to use as a lamp because the walls absorb most of the light. Therefore. for use as lamps. I prefer the arrange ments of Figs. 2 to 6, inclusive.

Fig. 2 illustrates a modification of my invention which is designed particularly to be operated directly through A. C. power mains and which is so designed as to be a good light radiator. In the arrangement shown in this figure the body of the discharge tube 20| is formed of a transparent material such as high temperature glass or quartz. As shown, it is in the form of a cylinder. At one end is attached the cathode cup 2I9 by any conventional means. This cup contains the mercury cathode pool 51, the inside walls of which are enameled where they may be touched by the arc. Cooling fins 202 are provided around the periphery of the cathode cup to prevent overheating. The first anode 255, which is attached to body 20| in the same way as the cathode cup. is also provided with cooling fins. The second anode 259 is contained within a chamber 202 attached to the opposite side of the rst anode from which body 20| is attached. The second anode is also provided with cooling iins 203. In this modification the A. C. power is supplied through transformer 2|0 which is ofthe voltage adjusting and current limiting type somewhat similar to the ignition transformer described for Fig. l.. One end of the secondary winding of this transformer is connected directly to anode 259 and the first anode 255 is connected to the same end of the secondary through the current limiting resistor 205. The other end of the secondary winding is connected directly to the cathode cup 2|9. The ignition transformer I 23 in this medification is connected through condenser 2|5 directly across the secondary of transformer 2|0. The condenser 2I5 acts not only as a phase advancer for the ignition transformer but also as a storage means for the main arc. In this mcdication when power is supplied to the tube through transformer 2|0 a high voltage is impressed between arc starter point 53vand the mercury cathode pool thus striking an-arc which establishes the main arc between the mercury cathode and thesecond anode.

I may, instead of the exact arrangement shown in Fig. 2, connect the primary winding of transformer |23 across the A. C. power input to transformer 2|0. Condenser 2|5 or an equivalent phase shifting means must be connected in series with the primary.

Fig. 3 illustrates a modification of the form of my invention shown in Fig. 2 in which a thermionic cathode 351 is provided instead of a liquid cathode as shown in Fig. 2. A pool of liquid mercury 51 is included within the tube for supplying the ions for the mercury arc discharge. A cathode shield 358 is provided to protect the thermionic cathode from ionic bombardment from the luminous arc. In this modification there is no outside connection provided for the first anode 355. Instead. a short cylinder of resistance material 360 connects the second anode and the iirst anode within the tube.

If two barriers with holes in line are interposed in the path of the arc the minimum voltage drop in the arc between cathode and anode is increased and may, for example, amount to about 20 volts per barrier. depending upon dimensions. Thus, by increasing the number of barriers any desired minimum arc voltage drop may be obtained. Three barriers may be used to obtain a normal minimum arc drop of 'l5 volts. If an anode voltage of 110 volts is applied to such a device then volts would be accounted for by the normal minimum arc drop and 35 volts would be accounted for by voltage regulation in the power supply circuits or by limiting of the arc through the holes in the barriers. Such a lamp can be connected directly across 110 volt circuit. To provide easy starting the barriers should be connected to one another successively and to the anode through relatively high resistances. Thus, the anode voltage would be applied to all the barriers until the starting of the arc changed the voltage distribution.

Fig. 4 represents such a modification of my device in which a plurality of barrier anodes 455 465 and 415 are provided in order to increase the total voltage drop through the discharge tube. The power supply transformer 4|0 has a multiple tap secondary, the individual taps of which are connected through the resistances 411, 419 and 48| to the successive barrier anodes. Condensers 415, 418, 480 and 482 may be provided between each successive electrode in order to prevent voltage surges but are not required. In this modification the high potential for the ignition arc between the arc starter point 53 and the mercury pool cathode is provided by means of the inductance capacity circuit 484-485. Series resistance 483 is provided in the arc starter point circuit to limit the arc starter current to a reasonable value.

Fig. 5 illustrates a modification of the structure shown in Fig. 4 wherein a thermionic cathode 351 and a cathode shield 358 are used in the same way as in the modification of Fig. 3.

Fig. 6 illustrates a further modification of the structure shown in Fig. 4 except that a double cathode has been provided for full-wave operation. At each alternate half cycle of the current supplied, one mercury path will act as a cathode and the other as the anode and at the intervening half cycles the functions will be reversed.

An arc discharge lamp, constructed according to this modification, would be more desirable than the previous modifications, in some insodium. My lamps may contain only gases such as neon, helium, argon, etc., either singly or in mixtures with either hot or cold Icathode discharges. Regardless of the gas or vapor, or mixture, used the discharge through holes in barriers enables me to increase the voltage drop in the arc and so obtain light resulting from ionization of all the gases and vapors or from multiple ionization of the gases and vapors and therefore I new and useful colors and intensities of light.

An arc discharge lamp, constructed according to my invention, has the following advantages:

(1) Due to current limiting of the arc through the barrier no ballast reactance or resistance is required as in the ordinary mercury arc lamps now in use with which I am familiar.

(2) Due to the high voltage drop in the arc a desirable light spectrum is obtained from the original atomic light sources and the light is absorbed less within the lamp4 itself because of the relatively low vapor pressure and density around the luminous part of the lamp. Furthermore, a more desirable light spectrum may be easily obtained with my invention by means of a mixture of gases within the tube.

(3) The arc through the hole gives an almost cylindrical source of light which is well adapted to directivity and focussing with reilectors, prisms, etc.

It should be distinctly understood that the present invention is not limited to the precise arrangements and designed features shown in the various figures since these have merely been illustrated for the purpose of setting forth the particulars of typical forms of the present invention.

' The barriers may be made of electrical insulating material for low power lamps. I prefer metal barriers primarily because of the high heat and electrical conductivity of metal which permits relatively high currents and which permits better control of potential distribution in and near the hole in the barrier.

I claim:

1. A gas discharge lamp comprising an evacuated casing having a mercury pool cathode at one end, an anode at the other end, means for establishing an arc discharge between the anode and cathode, means for increasing the voltage drop in the arc comprising an apertured barrier anode between the anode and cathode, the aperture providing a restricted arc discharge path and means for energizing said barrier anode.

2. A gas discharge lamp comprising an evacuated casing containing an ionizable gas and having a cathode at one end and an anode at the other end, means for establishing an arc discharge between the anode and cathode, means for increasing the voltage drop in the arc comprising an apertured barrier anode between the anode and cathode, the aperture providing a restricted arc discharge path and means for establishing an arc discharge between said barrier anode and said cathode.

3. A gasdischarge lamp comprising an evacuated casing having a cathode at one end, an anode at the other end and a barrier anode between said anode and cathode., means for establishing an arc discharge between the cathode and the anode, means for increasing the voltage drop in the arc comprising a4 restricted aperturev in said barrier anode through which the discharge must pass and means for energizing said barrier anode.

4. A gas discharge lamp comprising an evacuated casing having a mercury pool cathode at one end, an anode at the other end, a barrier anode between said anode and cathode, means for establishing an arc discharge between the cathode and the anode, means for increasing the voltage drop in the arc comprising a restricted aperture in said barrier anode through which the arc discharge must pass and means for establishing-an arc discharge between said barrier anode and said cathode.

5. A gas discharge lamp comprising an evacuated casing containing a mixture of ionizable gases having widely differing ionizing potentials and having therein an anode at one end, a cathode at the other end and an apertured barrier anode between the anode and cathode dividing the casing into two chambers, means for energizing said barrier anode, means for establishing an arc discharge between the cathode and anode through the aperture in the barrier anode, the current density in the aperture in the barrier anode being so adjusted that multiple ionization of the gas occurs.

6. A gas discharge lamp comprising an evacuated casing containing an ionizable gas having therein an anode at one end, a mercury pool cathode at the other end and an apertured barrier anode between the anode and cathode dividing the casing into two chambers, means for establishing an arc discharge between the cathode and anode through the aperture in the barrier anode and means for energizing said barrier anode, the current density in the aperture in ,the barrier anode being so adjusted that multiple ionization of the gas occurs.

7. A gas discharge lamp comprising an elongated evacuated casing containing a mixture of ionizable gases having widely differing ionizing potentials, a cathode .'at one end of said casing and an anode at the other end of said casing, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a barrier anode having a restricted opening therethrough in the path of said arc discharge and means for energizing said barrier anode.

8. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at one end of said casing, an anode at the other end of said casing, said casing also containing a gas having an ionizing potential widely diiiering from that of mercury vapor, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a barrier anode having a restricted opening therethrough in the path of said arc discharge, means for energizing said barrier anode and means for initiating said arc discharge, the current density in th'e aperture in said barrier anode being so adjusted that both said gas and said mercury vapor are ionized.

9. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at one end of said casing, an anode at the other end of said casing, said casing also containing a, gas having an ionizing potential widely differing from that of mercury vapor, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a barrier anode having a restricted opening therethrough in the path of said arc discharge, means for energizing said barrier anode and means for initiating said arc discharge, comprising a high resistance electrode mounted near the surface of the mercury pool and means for applying a potential between said cathode and said electrode, the current density in the aperture in said barrier anode being so adjusted that both said gas and said mercury vapor are ionized.

10. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at one end of said casing, an anode at the other end of said casing, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a barrier anode having a restricted opening therethrough in the path of said arc discharge, means for energizing said barrier anode and means for cooling said anode and said barrier anode.

11. A gas discharge lamp comprising an elongated evacuated casing containing a mixture of ionizable gases of widely differing ionizing p0- tentials, a thermionic cathode at one end of said casing, an anode at the other end of said casing, a source of energy connected to said anode and cathode and means for heating said cathode for generating an arc discharge between said anode and cathode, a barrier anode having a restricted opening therethrough in the path of said arc discharge and means for energizing said barrier anode, the current density in the aperture in said barrier anode being so adjusted that both of said gases are ionized.

12. A gas discharge lamp comprising an elongated evacuated casing containing an ionizable gas, a cathode at one end of said casing and an anode at the other end of said casing, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a plurality of barrier anodes each having a restricted opening therethrough in the path of said arc discharge of such size that the free passage of'said arc discharge is restricted whereby the voltage drop through said arc discharge is increased and means for energizing each of said barrier anodes.

13. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at one end of said casing, an anode at the other end-of said casing, a source of energy connected to said anode and cathode for generating an arc discharge therebetween, a plurality of barrier anodes each having a restricted opening therethrough in the path of said arc discharge of such size that the free passage of said arc discharge is restricted whereby the voltage drop through said arc discharge is increased, means for energizing each of said barrier anodes and means for initiating said arc discharge comprising a high resistance electrode mounted near the surface of the mercury pool and means for applying a potential between said cathode and said electrode.

14. A gas discharge lamp comprising an elongated evacuated casing containing a mixture of ionizable gases, a thermionic cathode at one end of said casing, an anode at the other end of said casing, a source oi energy connected to said anode and cathode for generating an arc discharge therebetween, a plurality of barrier anodes each having a restricted opening therethrough in the path of said arc disch rge, means for energizing each of said barrier anodes and means for initiating said arc discharge including means for heating said thermicnic cathode.

15. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at each end of said casing, a source of alternating current energy connected to said cathodes for generating an arc discharge therebetween, a plurality of barrier anodes each having a restricted opening therethrough in the path of said arc discharge whereby the voltage drop through said arc discharge is increased and means connected to said alternating current supply for energizing each of said barrier anodes.

16. A gas discharge lamp comprising an elongated evacuated casing, a mercury pool cathode at each end of said casing, a source of alternating current energy connected to said cathodes for generating an arc discharge therebetween, a plurality of barrier anodes each having a restricted opening therethrough in the path of said arc discharge whereby the voltage drop through said arc discharge is increased and means connected to said alternating current supply for energizing each of said barrier anodes, and means for initiating said arc discharge comprising a high resistance electrode mounted near the surface of each mercury pool cathode and means for applying a potential between each o! said cathodes and the electrode associated therewith.

CLARENCE W. EANSELL. 

